Sub-Zero Wolf MS24 User manual

General Information 2
Controls & Operation 8
Troubleshooting Guide 12
Component Access & Removal 25
Wiring Diagrams 31
subzero.com 800.222.7820
MS24 Standard Microwave
Service Manual

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MS24
PRECAUTIONS TO BE OBSERvED BEFORE
AND DURING SERvICING TO AvOID POSSIBLE
EXPOSURE TO EXCESSIvE mICROWAvE ENERGY
(a) Do not operate or allow the oven to be operated with the door open.
(b) Make the following safety checks on all ovens to be serviced before activating the magnetron or other microwave
source, and make repairs as necessary: (1) interlock operation, (2) proper door closing, (3) seal and sealing
surfaces (arcing, wear, and other damage), (4) damage to or loosening of hinges and latches, (5) evidence of
dropping or abuse.
(c) Before turning on microwave power for any service test or inspection within the microwave generating
compartments, check the magnetron, wave guide or transmission line, and cavity for proper alignment, integrity,
and connections.
(d) Any defective or misadjusted components in the interlock, monitor, door seal, and microwave generation and
transmission systems shall be repaired, replaced, or adjusted by procedures described in this manual before
the oven is released to the owner.
(e) A microwave leakage check to verify compliance with the Federal Performance Standard should be performed
on each oven prior to release to the owner.
BEFORE SERvICING
Before servicing an operative unit, perform a microwave emission check as per the Microwave Measure-
ment Procedure outlined in this service manual.
If microwave emissions level is in excess of the specified limit, contact WOLF immediately @
1-800-332-9513.
If the unit operates with the door open, service person should 1) tell the user not to operate the oven
and 2) contact WOLF and Food and Drug Administration's Center for Devices and Radiological Health
immediately.
Service personnel should informWOLF of any certified unit found with emissions in excess of 4mW/cm2.The
owner of the unit should be instructed not to use the unit until the oven has been brought into compliance.
DANGER CAUTION
HIGH vOLTAGE
Do not energize a microwave oven with the outer case cabinet removed, because a microwave oven
generates High Voltage in the circuit.
If you intend to operate the oven employing the high frequency switching power converter circuit, you should
take special precautions to avoid an electrical shock hazard.
The high voltage transformer, high voltage capacitor and high voltage diode have energized high voltage
potential approx. 8 KV.
The aluminium heat sink is connected to the switching power transistor Collector pole, and has an energized
high voltage potential approx. 650V peak.
DO NOT ACCESS THE HIGH VOLTAGE TRANSFORMER, HIGH VOLTAGE CAPACITOR, HIGH VOLTAGE
DIODE AND HEAT SINK WHEN THE POWER SUPPLY IS CONNECTED TO AN ELECTRICAL OUTLET.

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MS24
WARNING TO SERVICE PERSONNEL
Microwave ovens contain circuitry capable of pro-
ducing very high voltage and current, contact with
following parts
may result in a severe, possibly
fatal, electrical shock.
(Example)
High Voltage Capacitor, High Voltage Power
Transformer, Magnetron, High Voltage Rectifier
Assembly, High Voltage Harness etc..
Read the Service Manual carefully and follow all
instructions.
Before Servicing
1. Disconnect the power supply cord , and then
remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
WARNING:RISK OF ELECTRIC SHOCK.
DISCHARGE THE HIGH-VOLTAGE
CAPACITOR BEFORE SERVICING.
The high-voltage capacitor remains charged about 60
seconds after the oven has been switched off. Wait for
60 seconds and then short-circuit the connection of the
high-voltage capacitor (that is the connecting lead of the
high-voltage rectifier) against the chassis with the use of
an insulated screwdriver.
Whenever troubleshooting is performed the power supply
must be disconnected.It may in, some cases, be necessary
to connect the power supply after the outer case has been
removed, in this event,
1. Disconnect the power supply cord, and then remove
outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Disconnect the leads to the primary of the power
transformer.
5. Ensure that the leads remain isolated from other
components and oven chassis by using insulation
tape.
6. After that procedure, reconnect the power supply cord.
When the testing is completed,
1. Disconnect the power supply cord, and then remove
outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Reconnect the leads to the primary of the power
transformer.
5. Reinstall the outer case (cabinet).
6. Reconnect the power supply cord after the outer case
is installed.
7. Run the oven and check all functions.
After repairing
1. Reconnect all leads removed from components during
testing.
2. Reinstall the outer case (cabinet).
3. Reconnect the power supply cord after the outer case
is installed.
4. Run the oven and check all functions.
Microwave ovens should not be run empty. To test for the
presence of microwave energy within a cavity, place a cup
of cold water on the oven turntable, close the door and set
the power to HIGH and set the microwave timer for two (2)
minutes. When the two minutes has elapsed (timer at zero)
carefully check that the water is now hot.If the water remains
cold carry out Before Servicing procedure and re-examine
the connections to the component being tested.
When all service work is completed and the oven is fully
assembled, the microwave power output should be checked
and a microwave leakage test should be carried out.
Don't Touch !
Danger High Voltage

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MS24
MICROWAVE MEASUREMENT PROCEDURE
A. Requirements:
1) Microwave leakage limit (Power density limit): The power density of microwave radiation emitted by a microwave
oven should not exceed 1mW/cm2at any point 5cm or more from the external surface of the oven, measured prior to
acquisition by a purchaser, and thereafter (through the useful life of the oven), 5 mW/cm2at any point 5cm or more
from the external surface of the oven.
2) Safety interlock switches Primary interlock relay and door sensing switch shall prevent microwave radiation emission in
excess of the requirement as above mentioned, secondary interlock switch shall prevent microwave radiation emission
in excess of 5 mW/cm2at any point 5cm or more from the external surface of the oven.
B. Preparation for testing:
Before beginning the actual measurement of leakage, proceed as follows:
1) Make sure that the actual instrument is operating normally as specified in its instruction booklet.
Important:
Survey instruments that comply with the requirement for instrumentation as prescribed by the performance standard for
microwave ovens, 21 CFR 1030.10(c)(3)(i), must be used for testing.
2) Place the oven tray in the oven cavity.
3) Place the load of 275±15 ml (9.8 oz) of tap water initially at 20±5oC (68oF) in the center of the oven cavity.
The water container shall be a low form of 600 ml (20 oz) beaker with an inside diameter of approx. 8.5 cm (3-1/2 in.)
and made of an electrically nonconductive material such as glass or plastic.
The placing of this standard load in the oven is important not only to protect the oven, but also to insure that any leakage
is measured accurately.
4) Set the cooking control on Full Power Cooking Mode.
5) Close the door and select a cook cycle of several minutes. If the water begins to boil before the survey is completed,
replace it with 275 ml of cool water.
C. Leakage test:
Closed-door leakage test (microwave measurement)
1) Grasp the probe of the survey instrument and hold it perpendicular to the gap between the door and the body of the
oven.
2) Move the probe slowly, not faster than 1 in./sec. (2.5 cm/sec.) along the gap, watching for the maximum indication on
the meter.
3) Check for leakage at the door screen, sheet metal seams and other accessible positions where the continuity of the
metal has been breached (eg., around the switches, indicator, and vents).
While testing for leakage around the door pull the door away from the front of the oven as far as is permitted by the
closed latch assembly.
4) Measure carefully at the point of highest leakage and make sure that the highest leakage is no greater than 4mW/cm2,
and that the secondary interlock switch does turn the oven OFF before any door movement.
NOTE: After servicing, record data on service invoice and microwave leakage report.

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MS24
SERVICE MANUAL
MS24
FOREWORD
This Manual has been prepared to provide WOLF Service Personnel with
Operation and Service Information for the WOLF oven.
It is recommended that service personnel carefully study the entire text of
this manual so that they will be qualified to render satisfactory customer
service.
Check the interlock switches and the door seal carefully.Special attention
should be given to avoid electrical shock and microwave radiation hazard.
WARNING
Never operate the oven until the following points are ensured:
(A) The door is tightly closed.
(B) The door brackets and hinges are not defective.
(C) The door packing is not damaged.
(D) The door is not deformed or warped.
(E) There is no other visible damage with the oven.
Servicing and repair work must be carried out only by trained service
personnel.
DANGER
Certain initial parts are intentionally not grounded and present a
risk of electrical shock only during servicing. Service personnel -
Do not contact the following parts while the applianceis energized;
High Voltage Capacitor, PowerTransformer,Magnetron, High Voltage
Hig Voltage Harness;
If provided, Vent Hood, Fan assembly, Cooling FanMotor.
All thepartsmarked“*”onparts list areusedatvoltagesmorethan 250V.
Removal of the outer wrap gives access to voltage above 250V.
Allthepartsmarked“∆”onparts listmaycauseunduemicrowaveexpo -
sure, by themselves,or whentheyaredamaged,loosenedor removed.
MICROWAVE OVEN
Recitifer Assembly,
Wolf Appliance, Inc.
P.O. Box 44988
Madison, WI 53744-4988
Customer Care: 800.332.9513

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MS24
ITEM DESCRIPTION
Power Requirements 120 Volts / 13.8 Amperes/1650Watts
60 Hertz
Single phase, 3 wire grounded
Power Output 1200 watts (IEC-705 TEST PROCEDURE)
Operating frequency of 2450MHz
Case Dimensions Width 24"
Height 13-3/8"
Depth 19-1/8"
Cooking Cavity Dimensions Width 17-3/8"
2.0 Cubic Feet Height 10-1/2"
Depth 18-5/8"
Tray Size 15"
Control Complement Touch Control with Touch Glass
Clock ( 1:00 - 12:59 )
Timer (0 - 99 min. 99 seconds)
Microwave Power for Variable Cooking
Repetition Rate;
P-HI .................................................. Full power throughout the cooking time
P-90..................................................................... approx. 90% of Full Power
P-80..................................................................... approx. 80% of Full Power
P-70..................................................................... approx. 70% of Full Power
P-60..................................................................... approx. 60% of Full Power
P-50..................................................................... approx. 50% of Full Power
P-40..................................................................... approx. 40% of Full Power
P-30 .................................................................... approx. 30% of Full Power
P-20..................................................................... approx. 20% of Full Power
P-10..................................................................... approx. 10% of Full Power
P-0..................................................... No power throughout the cooking time
Cavity Light Yes
Safety Standard UL Listed FCC Authorized
DHHS Rules, CFR, Title 21, Chapter 1, Subchapter J
SPECIFICATION
GENERAL INFORMATION
GROUNDING INSTRUCTIONS
This oven is equipped with a three prong grounding plug. It must be plugged into a wall receptacle that is properly installed
and grounded in accordance with the National Electrical Code and local codes and ordinances.
In the event of an electrical short circuit, grounding reduces the risk of electric shock by providing an escape wire for the
electric current.
WARNING: Improper use of the grounding plug can result in a risk of electric shock.
Electrical Requirements
The electrical requirements are a 120 volt 60 Hz, AC only,
15 or 20 amp. fused electrical supply. It is recommended that a separate circuit serving only this appliance be provided.
When installing this appliance, observe all applicable codes and ordinances.
A short power-supply cord is provided to reduce risks of becoming entangled in or tripping over a longer cord.
Where a two-pronged wall-receptacle is encountered, it is the personal responsibility and obligation of the customer to
contact a qualified electrician and have it replaced with a properly grounded three-pronged wall receptacle or have a
grounding adapter properly grounded and polarized. If the extension cord must be used, it should be a 3-wire, 15 amp. or
higher rated cord. Do not drape over a countertop or table where it can be pulled on by children or tripped over accidentally.
Popcorn, Beverage, Baked Potatoe, Frozen Entree, Bacon, Frozen Vegetables,
Soften, Reheat, Melt, Auto Defrost, WOLF Gourmet, manual Defrost, Keep
Warm, Settings, Add Minute, Clock, Start/Quick On, Numbers, Timer, Stop/Clear.
TOUCH CONTROL

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MS24
CAUTION: DO NOT UNDER ANY CIRCUMSTANCES CUT OR
REMOVE THE ROUND GROUNDING PRONG FROM
THIS PLUG.
OVEN DIAGRAM
NOTE:
Some one-touch cooking features such as "EXTRA MINUTE" are disabled
after three minutes when the oven is not used. These features are automati-
cally enabled when the door is opened and closed or the STOP/ CLEAR pad
is pressed.
TOUCH CONTROL
3-Pronged
Plug
Grounded
Receptacle Box
Grounding Pin
3-Pronged Receptacle
One touch
door open pad
Oven door
with see-through
window
Interactive display
Safety door
latches
Rating plate
Door hinges
Door seals and
sealing surfaces
Turntable
Ventilation
openings (rear)
Oven light
Waveguide cover
Touch Glass
Control Panel
Menu label
Turntable support
Power supply cord
Ventilation openings

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MS24
OPERATION
DESCRIPTION OF OPERATING SEQUENCE
The following is a description of component functions dur-
ing oven operation.
OFF CONDITION
Closing the door activates the door sensing switch and
secondary interlock switch. (In this condition, the monitor
switch contacts are opened.)
When oven is plugged in, 120 volts A.C. is supplied to the
control unit. (Figure O-1).
1. The display will show flashing "WELCOME TOUCH
CLEAR AND TOUCH CLOCK TO SET TIME"
To set any program or set the clock, you must first touch
the STOP/CLEAR pad. The display will clear, and " : "
will appear.
COOKING CONDITION
First program the power level by touching the POWER
LEVEL pad then a number pad. (Touch POWER LEVEL
pad twice to choose high.) Then you can enter the cooking
time by touching the number pads.
When the START pad is touched, the following operations
occur:
1. The contacts of relays are closed and components
connected to the relays are turned on as follows.
(For details, refer to Figure O-2)
RELAY CONNECTED COMPONENTS
RY-1 oven lamp/turntable motor/fan motor
RY-2 power transformer
2. 120 volts A.C. is supplied to the primary winding of the
power transformer and is converted to about 3.3 volts
A.C. output on the filament winding, and approximately
2370 volts A.C. on the high voltage winding.
3. The filament winding voltage heats the magnetron
filament and the H.V. winding voltage is sent to a voltage
doubler circuit.
4. The microwave energy produced by the magnetron is
channelled through the waveguide into the cavity feed-
box, and then into the cavity where the food is placed
to be cooked.
5. Upon completion of the cooking time, the power
transformer, oven lamp, etc. are turned off, and the
generation of microwave energy is stopped. The oven
will revert to the OFF condition.
6. When the door is opened during a cook cycle, the monitor
switch, door sensing switch, primary interlock switch, relay
(RY1) and secondary interlock relay are activated with
the following results. The circuits to the turntable motor,
the cooling fan motor, and the high voltage components
are de-energized, the oven lamp remains on, and the
digital read-out displays the time still remaining in the
cook cycle when the door was opened.
7. The monitor switch electrically monitors the operation
of the primary interlock switch and secondary interlock
relay and is mechanically associated with the door so
that it will function in the following sequence.
(1) When the door opens from the closed position, the
secondary interlock relay (RY2) and primary interlock
switch open their contacts. And contacts of the relay
(RY1) remains closed.Then the monitor switch contacts
close.
(2) When the door is closed from the open position, the
monitor switch contacts open first. Then the contacts
of the primary interlock switch and door sensing switch
close. And contacts of the relay (RY1) open.
If the primary interlock switch and secondary interlock relay
(RY2) fail with the contacts closed when the door is opened,
the closing of the monitor switch contacts will form a short
circuit through the monitor fuse, primary interlock switch,
relay (RY1) and secondary interlock relay (RY2), causing
the monitor fuse to blow.
POWER LEvEL P-0 TO P-90 COOKING
When Variable Cooking Power is programmed, the 120
volts A.C.is supplied to the power transformer intermittently
through the contacts of relay (RY-2) which is operated by
the control unit within a 32 second time base. Microwave
power operation is as follows:
VARI-MODE ON TIME OFF TIME
Power 10(P-HI) 32 sec. 0 sec.
(100% power)
Power 9(P-90) 30 sec. 2 sec.
(approx. 90% power)
Power 8(P-80) 26 sec. 6 sec.
(approx. 80% power)
Power 7(P-70) 24 sec. 8 sec.
(approx. 70% power)
Power 6(P-60) 22 sec. 10 sec.
(approx. 60% power)
Power 5(P-50) 18 sec. 14 sec.
(approx. 50% power)
Power 4(P-40) 16 sec. 16 sec.
(approx. 40% power)
Power 3(P-30) 12 sec. 20 sec.
(approx. 30% power)
Power 2(P-20) 8 sec. 24 sec.
(approx. 20% power)
Power 1(P-10) 6 sec. 26 sec.
(approx. 10% power)
Power 0(P-0) 0 sec. 32 sec.
(0% power)
Note: The ON/OFF time ratio does not correspond with the
percentage of microwave power, because approx. 2
seconds are needed for heating of the magnetron
filament.

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MS24
SENSOR COOKING CONDITION
Using the SENSOR function, food is cooked without figur-
ing time, power level or quantity. When the oven senses
enough steam from the food, it relays the information to its
microprocessor which will calculate the remaining cooking
time and power level needed for best results. When the food
is cooked, water vapor is developed. the sensor "senses"
the vapor and its resistance increase gradually. When the
resistance reaches the value set according to the menu,
supplementary cooking is started.
The time of supplementary cooking is determined by experi-
ment with each food category and inputted into the LSI. An
example of how sensor works: (Potatoes)
1. Potatoes at room temperature. Vapor is emitted very
slowly.
MICROWAVE
2.Heat Potatoes. Moisture and humidity is emitted very
rapidly. You can smell the aroma as it cooks.
MICROWAVE
AH SENSOR
3.Sensor detects moisture and humidity and calculates
cooking time and variable power.
Cooking Sequence.
1. Touch one of the SENSOR pads (example REHEAT).
NOTE: The oven should not be operated on sensor
immediately after plugging in the unit. Wait two
minutes before cooking on SENSOR.
2. The coil of shut-off relay (RY-1) is energized, the turntable
motor are turned on, but the power transformer is not
turned on.
3. After about 16 seconds, the cook relay (RY-2) is
energized. The power transformer is turned on,
microwave energy is produced and first stage is started.
The 16 seconds is the cooling time required to remove
any vapor from the oven cavity and sensor.
NOTE: During this first stage, do not open the door or
touch STOP/CLEAR pad.
4. When the sensor detects the vapor emitted from the
food, the display switches over to the remaining cooking
time and the timer counts down to zero.
At this time, the door may be opened to stir, turn or
season food.
5. When the timer reaches zero, an audible signal sounds.
The shut-off relay and cook relay are de-energized and
the power transformer, oven lamp, etc. are turned off.
6. Opening the door or touching the STOP/CLEAR pad,
the time of the day will reappear on the display and the
oven will revert to an OFF condition. When the timer
reaches zero, an audible signal sounds.

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MS24
Figure O-2 Oven Schematic - Cooking Condition
Figure O-1 Oven Schematic - Off Condition
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED
2. CLOCK APPEARS ON DISPLAY
SCHEMATIC
3. VARIABLE COOKING CONTROL "HIGH"
2. COOKING TIME PROGRAMMED
1. DOOR CLOSED
NOTE: CONDITION OF OVEN
4. "START" PAD TOUCHED
NOTES:
1.CIRCUITS SUBJECT TO CHANGE WITHOUT NOTICE.
2.TERMINAL WITH PROJECTION OR OPPOSITE BLUE MARK ON LAMP SOCKET
MUST BE CONNECTED TO NEUTRAL WIRE.
3. ONLY CERTAIN MODELS USE THE ABSOLUTE HUMIDITY SENSOR.
4. POWER TRANSFORMER TOP (FINISH LEAD) TERMINAL MUST BE CONNECTED TO THE NEUTRAL (WHT ) WIRE.
CAVITY
TEMPERATURE
FUSE
120VAC
60Hz
COM.
RED
RED
WHT
WHT
WHT
GRY
BRN
WHT
WHT
WHT
ORG
RED
WHT
WHT
GRN
N.O.
B2
B1
CONTROL UNIT
MAGNETRON
TEMPERATURE
FUSE
N.O.
(RY2)
COM.
DOOR
SENSING
SWITCH
TTM FM
OL
TURN
TABLE
MOTOR
FAN
MOTOR
OVEN
LAMP
MONITOR
SWITCH
PRIMARY
INTERLOCK
SWITCH
POWER
TRANSFORMER
MAGNETRON
HIGH
VOLTAGE
CAPACITOR
xx µF
ORG
WHT
SECONDARY
INTERLOCK
RELAY
ORG
BRN
ORG
ORG
RED
GRY
GRY
GND
WHT
F3
F2
F1
SENSOR
(RY1)
OVEN
LAMP
RELAY
COM. N.O.
HUMIDITY
COM.
N.C.
HIGH
VOLTAGE
RECTIFIER
ORG
H
N
RED
RED
PNK
GRN
GRN
GRN
GRN
C3
C2
C1
BLK
WHT
NOISE
FILTER
MONITOR
FUSE (20A)
R2
"TO LOAD"
"TO LOAD"
"TO SOURCE" "TO SOURCE"
NOTES:
1.CIRCUITS SUBJECT TO CHANGE WITHOUT NOTICE.
2.TERMINAL WITH PROJECTION OR OPPOSITE BLUE MARK ON LAMP SOCKET
MUST BE CONNECTED TO NEUTRAL WIRE.
3. ONLY CERTAIN MODELS USE THE ABSOLUTE HUMIDITY SENSOR.
4. POWER TRANSFORMER TOP (FINISH LEAD) TERMINAL MUST BE CONNECTED TO THE NEUTRAL ( WHT ) WIRE.
CAVITY
TEMPERATURE
FUSE
120VAC
60Hz
COM.
RED
RED
WHT
WHT
WHT
GRY
BRN
WHT
WHT
WHT
ORG
RED
WHT
WHT
GRN
N.O.
B2
B1
CONTROL UNIT
MAGNETRON
TEMPERATURE
FUSE
N.O.
(RY2)
COM.
DOOR
SENSING
SWITCH
TTM FM
OL
TURN
TABLE
MOTOR
FAN
MOTOR
OVEN
LAMP
MONITOR
SWITCH
PRIMARY
INTERLOCK
SWITCH
POWER
TRANSFORMER
MAGNETRON
HIGH
VOLTAGE
CAPACITOR
xx µF
ORG
WHT
SECONDARY
INTERLOCK
RELAY
ORG
BRN
ORG
ORG
RED
GRY
GRY
GND
WHT
F3
F2
F1
SENSOR
(RY1)
OVEN
LAMP
RELAY
COM. N.O.
HUMIDITY
COM.
N.C.
HIGH
VOLTAGE
RECTIFIER
ORG
H
N
RED
RED
PNK
GRN
GRN
GRN
GRN
C3
C2
C1
BLK
WHT
NOISE
FILTER
MONITOR
FUSE (20A)
R2
"TO LOAD"
"TO LOAD"
"TO SOURCE" "TO SOURCE"

Page 11
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MS24
DESCRIPTION AND FUNCTION OF COMPONENTS
DOOR OPEN MECHANISM
The door is opened by pushing the open button on the con-
trol panel, refer to the Figure D-1. When the open button is
pushed, the open button pushes up the switch lever, and
then the switch lever pushes up the latch head. The latch
heads are moved upward and released from latch hook.
Now the door will open.
Figure D-1. Door Open Mechanism
DOOR SENSING AND PRIMARY INTERLOCK
SWITCHES
The primary interlock switch is mounted in the lower position
of the latch hook and the door sensing switch in the second-
ary interlock system is mounted in the upper position of the
latch hook. They are activated by the latch heads on the
door. When the door is opened, the switches interrupt the
power to all high voltage components. A cook cycle cannot
take place until the door is firmly closed thereby activating
both interlock switches. The secondary interlock system
consists of the door sensing switch and secondary interlock
relay located on the control circuit board.
MONITOR SWITCH
The monitor switch is activated (the contacts opened) by the
latch head on the door while the door is closed. The switch
is intended to render the oven inoperative, by means of
blowing the monitor fuse, when the contacts of the second-
ary interlock relay (RY2) and primary interlock switch fail to
open when the door is opened.
Functions:
1. When the door is opened, the monitor switch contact
close (to the ON condition) due to their being normally
closed. At this time the secondary interlock relay (RY2)
and primary interlock switch are in the OFF condition
(contacts open) due to their being normally open contact
switches.
2. As the door goes to a closed position, the monitor switch
contacts are first opened and then the door sensing
switch and the primary interlock switch contacts close.
(On opening the door, each of these switches operate
inversely.)
3. If the door is opened, and the secondary interlock relay
(RY2) and primary interlock switch contacts fail to open,
the monitor fuse blows simultaneously with closing of the
monitor switch contacts.
CAUTION: BEFORE REPLACING A BLOWN MONITOR
FUSE TEST THE DOOR SENSING SWITCH,
SECONDARY INTERLOCK RELAY (RY2), RE-
LAY (RY1), PRIMARY INTERLOCK SWITCH
AND MONITOR SWITCH FOR PROPER
OPERATION. (REFER TO CHAPTER "TEST
PROCEDURE").
NOTE: MONITOR FUSE AND MONITOR SWITCH ARE
REPLACED AS AN ASSEMBLY.
TURNTABLE MOTOR
The turntable motor rotates the turntable located on the
bottom of the oven cavity, so that the foods on the turntable
cook evenly during cooking.The turntable may turn in either
direction.
COOLING FAN MOTOR
The cooling fan motor drives a blade which draws external
cool air. This cool air is directed through the air vanes sur-
rounding the magnetron and cools the magnetron. This air
is channeled through the oven cavity to remove steam and
vapors given off from the heating foods. It is then exhausted
through the exhausting air vents at the oven cavity.
CAVITY TEMPERATURE FUSE
The cavity temperature fuse located on the top of the oven
cavity, is designed to prevent damage to the oven by fire.
If the food load is overcooked, by either error in cook time
or defect in the control unit, the cavity temperature fuse
will open.
Under normal operation, the cavity temperature fuse remains
closed. However, when abnormally high temperatures are
reached within the oven cavity, the cavity temperature fuse
will open at 302OF(150OC) causing the oven to shut down.
NOTE: This is a fuse. It does not reset.
MONITOR FUSE
1. The monitor fuse blows when the contacts (COM-NO) of
the primary interlock relay (RY2) and secondary interlock
switch remain closed with the oven door open and when
the monitor switch closes.
2. If the wire harness or electrical components are short-
circuited, this monitor fuse blows to prevent an electric
shock or fire hazard.
Magnetron TEMPERATURE FUSE
The magnetron temperature fuse located near the magne-
tron is designed to prevent damage to the magnetron if an
over heated condition develops in the tube due to cooling
fan failure, obstructed air guide, dirty or blocked air intake,
etc.
Under normal operation, the magnetron temperature fuse
remains closed. However, when abnormally high tempera-
tures are reached within the magnetron, the magnetron
temperature fuse will open at 302OF(150OC) causing the
oven to shut down.
NOTE: This is a fuse. It does not reset.
Door S ens ing
S witch
Monitor S witch
S witch Lever
P rimary Interlock
S witch
Latch Heads
Door

Page 12
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MS24
TROUBLESHOOTING GUIDE
Never touch any part in the circuit with your hand or an uninsulated tool while the power supply is connected.
When troubleshooting the microwave oven, it is helpful to follow the Sequence of Operation in performing the checks. Many
of the possible causes of trouble will require that a specific test be performed. These tests are given a procedure letter
which will be found in the "Test Procedure "section.
IMPORTANT: If the oven becomes inoperative because of a blown monitor fuse, check the primary switch, and monitor
switch, before replacing the monitor fuse. If the monitor fuse is replaced, the monitor switch must also be
replaced. Use part FFS-BA016/KIT as an assembly.
IMPORTANT: Whenever troubleshooting is performed with the power supply cord disconnected. It may in, some cases,
be necessary to connect the power supply cord after the outer case has been removed, in this event,
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Disconnect the leads to the primary of the power transformer.
5. Ensure that the leads remain isolated from other components and oven chassis by using insulation tape.
6. After that procedure, reconnect the power supply cord.
When the testing is completed
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Reconnect the leads to the primary of the power transformer.
5. Reinstall the outer case (cabinet).
6. Reconnect the power supply cord after the outer case is installed.
7. Run the oven and check all functions.

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MS24
A mAGNETRON ASSEmBLY TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
TEST PROCEDURES
PROCEDURE
LETTER COmPONENT TEST
CK = Check / RE = Replace
SHORT IN POWER CORD SHORT OR OPENED WIRING MAGNETRON POWER TRANSFORMER H.V. RECTIFIER ASSEMBLY HIGH VOLTAGE CAPACITOR CAVITY TEMPERATURE FUSE
MAGNETRON TEMP FUSE
SECONDARY INTERLOCK SYSTEM PRIMARY INTERLOCK RELAY MONITOR SWITCH
BLOWN MONITOR SWITCH TEST
COOLING FAN MOTOR TURNTABLE MOTOR TOUCH CONTROL PANEL WRONG OPERATION LOW VOLTAGE DIRTY OVEN CAVITY RELAY (RY1)
AH SENSOR
Home fuse or circuit breaker blows when
power cord is plugged into wall receptacle.
Monitor fuse blows when power cord is
plugged into wall receptacle.
Any letters or indicators do not appear in
display when power cord is first plugged
into wall outlet.
Display does not operate properly when
STOP/CLEAR key is touched. (Buzzer
should sound and ":" or time of day
should appear in display.)
Oven lamp does not light when door is
opened.
Oven lamp does not go out when door is
closed.
Oven lamp lights but fan motor and
turntable motor do not operate.
Oven does not go into cook cycle when
START pad is touched
Oven seems to be operating but little or
no heat is produced in oven load. (Food
incompletely cooked or not cooked at all
at end of cook cycle.)
Oven goes into a cook cycle but
extremely uneven heating is produced in
oven load (food).
Oven does not cook properly when
programmed for P-50/ 50 PERCENT
mode. (Operates properly on P-HI/ 100
PERCENT mode.)
Oven goes into Defrost but food
is not defrosted well.
AH sensor does not end during Sensor
cooking condition. (Oven does not shut
off after a cup of water is boiling by
sensor cooking.)
Oven stops at 16 sec. or error displays
after starting.
RE RE
ABC D EEF F G
RE RE
H
CK CK
IJ
TEST PROCEDURE
POSSIBLE CAUSE
AND
DEFECTIVE PARTS
COOKING
CONDITION
CONDITION
PROBLEM
OFF
CONDITION
SENSOR
COOKING
CONDITION
CK KL
COMPU DEFROST TEST NOISE FILTER
G

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MS24
B POWER TRANSFORmER TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Disconnect the primary input terminals and measure the resistance of the transformer with an
ohmmeter. Check for continuity of the coils with an ohmmeter. On the R x 1 scale, the resistance
of the primary coil should be less than 1 ohm and the resistance of the high voltage coil should be
approximately 90 ohms; the resistance of the filament coil should be less than 1 ohm.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
(HIGH VOLTAGES ARE PRESENT AT THE HIGH VOLTAGE TERMINAL, SO DO NOT ATTEMPT TO
MEASURE THE FILAMENT AND HIGH VOLTAGE.)
TEST PROCEDURES
PROCEDURE
LETTER COmPONENT TEST
4. To test for an open filament, isolate the magnetron from the high voltage circuit. A continuity check
across the magnetron filament leads should indicate less than 1 ohm.
5. To test for a shorted magnetron, connect the ohmmeter leads between the magnetron filament leads
and chassis ground. This test should indicate an infinite resistance. If there is little or no resistance
the magnetron is grounded and must be replaced.
6. Reconnect all leads removed from components during testing.
7. Reinstall the outer case (cabinet).
8. Reconnect the power supply cord after the outer case is installed.
9. Run the oven and check all functions.
mICROWAvE OUTPUT POWER
The following test procedure should be carried out with the microwave oven in a fully assembled condi-
tion (outer case fitted).
HIGH VOLTAGES ARE PRESENT DURING THE COOK CYCLE, SO EXTREME CAUTION SHOULD
BE OBSERVED.
Power output of the magnetron can be measured by performing a water temperature rise test. This
test should only be used if above tests do not indicate a faulty magnetron and there is no defect in the
following components or wiring: silicon rectifier, high voltage capacitor and power transformer. This test
will require a 16 ounce (453cc) measuring cup and an accurate mercury thermometer or thermocouple
type temperature tester. For accurate results, the following procedure must be followed carefully:
1. Fill the measuring cup with 16 oz. (453cc) of tap water and measure the temperature of the water
with a thermometer or thermocouple temperature tester. Stir the thermometer or thermocouple
through the water until the temperature stabilizes. Record the temperature of the water.
2. Place the cup of water in the oven. Operate oven at POWER 10(HIGH) selecting more than 60
seconds cook time. Allow the water to heat for 60 seconds, measuring with a stop watch, second
hand of a watch or the digital read-out countdown.
3. Remove the cup from the oven and again measure the temperature, making sure to stir the
thermometer or thermocouple through the water until the maximum temperature is recorded.
4. Subtract the cold water temperature from the hot water temperature. The normal result should be
38 to 78oF(21 to 42.6oC) rise in temperature. If the water temperatures are accurately measured
and tested for the required time period the test results will indicate if the magnetron tube has low
power output (low rise in water temperature) which would extend cooking time or high power output
(high rise in water temperature) which would reduce cooking time. Because cooking time can be
adjusted to compensate for power output, the magnetron tube assembly should be replaced only if
the water temperature rise test indicates a power output well beyond the normal limits. The test is
only accurate if the power supply line voltage is 120 volts and the oven cavity is clean.

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MS24
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
NOTE: Be sure to use an ohmmeter that will supply a forward bias voltage of more than 6.3
volts.
C HIGH VOLTAGE RECTIFIER TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Isolate the rectifier from the circuit. Using the highest ohm scale of the meter, read the resistance
across the terminals and observe, reverse the leads to the rectifier terminals and observe meter
reading. If a short is indicated in both directions, or if an infinite resistance is read in both directions,
the rectifier is probably defective and should be replaced.
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. If the capacitor is open, no high voltage will be available to the magnetron. Disconnect input leads
and check for short or open between the terminals using an ohmmeter.
Checking with a high ohm scale, if the high voltage capacitor is normal, the meter will indicate
continuity for a short time and should indicate an open circuit once the capacitor is charged. If the
above is not the case, check the capacitor with an ohmmeter to see if it is shorted between either
of the terminals and case. If it is shorted, replace the capacitor.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
D HIGH VOLTAGE CAPACITOR TEST
E CAVITY TEMPERATURE FUSE TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. A continuity check across the cavity temperature fuse terminals should indicate a closed circuit
unless the temperature of the cavity temperature fuse reaches approximately 302OF(150OC). An
open cavity temperature fuse indicates overheating of the oven, exchange the cavity temperature
fuse and check inside of oven cavity and for improper setting of cooking time or operation of control
unit. Check for restricted air flow through the vent holes of the oven cavity, especially the cooling
fan and air guide.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
MAGNETRON TEMPERATURE FUSE TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. A continuity check across the magnetron temperature fuse terminals should indicate a closed circuit
unless the temperature of the magnetron temperature fuse reaches approximately 302OF(150OC).
An open magnetron temperature fuse indicates overheating of the magnetron. Check for restricted
air flow to the magnetron, especially the cooling fan air guide.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.

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MS24
TEST PROCEDURES
PROCEDURE
LETTER COmPONENT TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Isolate the switch and connect the ohmmeter to the common (COM.) and normally open (NO) terminal
of the switch. The meter should indicate an open circuit with the door open and a closed circuit with
the door closed. If improper operation is indicated, replace the primary interlock switch.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
SECONDARY INTERLOCK SYSTEm TEST
DOOR SENSING SWITCH
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Isolate the switch and connect the ohmmeter to the common (COM.) and normally open (NO)
terminal of the switch. The meter should indicate an open circuit with the door open and a closed
circuit with the door closed. If improper operation is indicated, replace the door sensing switch.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
NOTE: If the door sensing switch contacts fail in the open position and the door is closed, the cooling
fan, turntable and oven light will be activated by RY1.
SECONDARY INTERLOCK RELAY (RY2)
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Disconnect two (2) wire leads from the male tab terminals of the Secondary Interlock Relay. Check
the state of the relay contacts using a ohmmeter. The relay contacts should be open. If the relay
contacts are closed, replace the circuit board entirely or the relay itself.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
8. Run the oven and check all functions.
CAUTION: IFTHETEMPERATURE FUSE INDICATES AN OPEN CIRCUIT AT ROOMTEMPERATURE,
REPLACE TEMPERATURE FUSE.
F PRImARY INTERLOCK SWITCH TEST

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MS24
8. Run the oven and check all functions.
TEST PROCEDURES
PROCEDURE
LETTER COmPONENT TEST
1. Key Unit.
Please note that key unit is projected capacitive touch technology. Touching the keyglass surface
changes a key pad sensor's local electric field to activate a key action. The amount of finger
flesh's needed to trigger key activation is ~10mm diameter surface contact to the glass surface.
You should not press hard to active a key; only a light touch is needed to change the pad's local
electric field.
a) Run the oven and check all functions.
The following symptoms indicate a defective key unit.
b) When lightly touching a fingertip to any pad and one or more keys do not respond.
c) When lightly touching a fingertip to any pad and only nearby keys respond.
d) When any pad only responds when touch with excessive flesh like a large thumb (more than
20mm diameter of surface contact to the glass surface).
2. Control Unit
The following symptoms indicate a defective control unit.
2-1 In connection with pads.
a) when touch any keypad and there is no key response. Check if key cable is unplugged between
control unit and key unit. Check if key cable end is fully seating into the key unit's connector.
H TOUCH CONTROL/TOUCH GLASS TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Before performing this test, make sure that the primary interlock switch and the secondary interlock
relay are operating properly, according to the above Switch Test Procedure. Disconnect the wire
lead from the monitor switch (COM) terminal. Check the monitor switch operation by using the
ohmmeter as follows. When the door is open, the meter should indicate a closed circuit. When the
monitor switch actuator is pushed by a screw driver through the lower latch hole on the front plate
of the oven cavity with the door opened (in this condition the plunger of the monitor switch is pushed
in), the meter should indicate an open circuit. If improper operation is indicated, the switch may
be defective. After testing the monitor switch, reconnect the wire lead to the monitor switch (COM)
terminal and check the continuity of the monitor circuit.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
G mONITOR SWITCH TEST
P rimary
Interlock S witch Monitor S witch
S crew Driver
Ohmmeter
R ed White/ White

Page 18
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MS24
2-2 In connection with indicators
a) At a certain digit, all or some segments do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light.
d) The corresponding segments of all digits do not light up; or they continue to light up.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.
2-3 Other possible problems caused by defective control unit.
a) Buzzer does not sound or continues to sound.
b) Clock does not operate properly.
c) Cooking is not possible.
3. If the Key unit or the Control unit is defective.
1) Disconnect the power supply cord, and then remove outer case.
2) Open the door and block it open.
3) Discharge high voltage capacitor.
4) Replace the Control unit assembly.
5) Reconnect all leads removed from components during testing.
6) Re-install the outer case (cabinet).
7) Reconnect the power supply cord after the outer case is installed.
8) Run the oven and check all functions.
TEST PROCEDURES
PROCEDURE
LETTER COmPONENT TEST

Page 19
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MS24
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
COMPU DEFROST TEST
WARNING : The oven should be fully assembled before following procedure.
(1) Place one cup of water in the center of the turntable tray in the oven cavity.
(2) Close the door, touch the Defrost pad and touch the number pad 5 twice.
Then touch the start pad.
(3) The oven is in Compu Defrost cooking condition.
(4) The oven will operate as follows
1ST STAGE 2ND STAGE
WEIGHT LEVEL TIME LEVEL TIME
0.5lb 70% 30sec. 40% 15sec.
(5) If improper operation is indicated, the control unit is probably defective and should be checked.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Disconnect the leads to the primary of the power transformer.
5. Ensure that these leads remain isolated from other components and oven chassis by using insulation
tape.
6. After that procedure, re-connect the power supply cord.
7. Remove the outer case and check voltage between Pin No. 1 of the 2 pin connector (A) and the
common terminal of the relay RY1 on the control unit with an A.C. voltmeter.
The meter should indicate 120 volts, if not check oven circuit.
RY1 and RY2 Relay Test
These relays are operated by D.C. voltage
Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation.
DC. voltage indicated ............. Defective relay.
DC. voltage not indicated ........ Check diode which is connected to the relay coil. If diode is good,
control unit is defective.
RELAY SYMBOL OPERATIONAL VOLTAGE CONNECTED COMPONENTS
RY1 Approx. 24.0V D.C. Oven lamp / Turntable motor / Cooling fan motor
RY2 Approx. 23.0V D.C. Power transformer
8. Disconnect the power supply cord, and then remove outer case.
9. Open the door and block it open.
10. Discharge high voltage capacitor.
11. Reconnect all leads removed from components during testing.
12. Re-install the outer case (cabinet).
13. Reconnect the power supply cord after the outer case is installed.
14. Run the oven and check all functions.
J
I RELAY TEST
1. Disconnect the power supply cord, and then remove outer case.

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MS24
Checking the initial sensor cooking condition
Warning: The oven should be fully assembled before following procedure.
1) The oven should be plugged in at least two minutes before sensor cooking.
2) Room temperature should not exceed 95oF(35oC).
3) The unit should not be installed in any area where heat and steam are generated. The unit should
not be installed for example, next to conventional surface unit. Refer to the "INSTALLATION
INSTRUCTIONS" of the operational manual.
(4) Exhaust vents are provided on the back of the unit for proper cooling and air flow in the cavity. To
permit adequate ventilation, be sure to install so as not to block these vents. There should be some
space for air circulation.
(5) Be sure the exterior of the cooking container and the interior of the oven are dry. Wipe off any
moisture with dry cloth or paper towel.
(6) The Sensor works with food at normal storage temperature. For example, chicken pieces would be
at refrigerator temperature and canned soup at room temperature.
(7) Avoid using aerosol sprays or cleaning solvents near the oven while using Sensor settings. The
sensor will detect the vapor given of by the spray and turn off before food is properly cooked.
(8) If the sensor has not detected the vapor of the food, ERROR will apear and the oven will shut off.
Water load cooking test
Warning: The oven should be fully assembled before following procedure.
Make sure the oven the oven has been plugged in at least two minutes before checking sensor cook
operation . the cabinet should be installed and screws tightened.
(1) The oven should be plugged in at least two minutes before sensor cooking
(2) Fill approximately 200 milliliters (7.2 oz) of tap water in 1000 milliliters measuring cup.
(3) Place the container on the center of tray in the oven cavity.
(4) Close the door.
(5) Touch the STOP/CLEAR pad once, clock pad once, power level pad twice, start pad once, "1' pad
once and "3" pad once. Now, the oven is in the sensor cooking condition and "TEST", "SENSOR" and
"COOK" will appear in the display.
(6) The oven will operate for the first 16 seconds, without generating microwave energy.
NOTE: ERROR will appear if the door is opened or STOP/CLEAR pad is touched during the first
stage of sensor cooking.
(7) After approximately 16 seconds, microwave energy is produced.
If ERROR is displayed, replace the AH sensor or check the control unit, refer to explaination below. If
the oven stops after 5 minutes and ERROR is displayed, check the parts except for the AH sensor.
K AH SENSOR TEST
TEST PROCEDURES
PROCEDURE
LETTER COmPONENT TEST